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qinglong.1397
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Hi, guys. I want to do some research on quantum gravity. I know that there are two theories achieving some success in this direction. Do you know something about that? I want to learn something about that. Thank you!
Kevin_Axion said:There are more than two theories, you've just only heard of two.
marcus said:Qing, there is a third approach called CDT which is simpler than the other two.
To begin to understand quantum gravity, I suggest you first try to understand CDT.
There is a good magazine article that makes it simple. This was in the Scientific American magazine. I always keep the link to it in my signature at the end of the message.
http://www.signallake.com/innovation/SelfOrganizingQuantumJul08.pdf
Read that first. Then I (or anyone else here) can tell you about LQG. And other people can tell you about String.
But please first this CDT article will explain that in quantum theory things can have uncertainty, and quantum gravity is about the uncertainty of geometry. We are all used to geometry being sharp, clear, fixed, unchanging according to definite laws (like the angles of a triangle add up to 180 degrees). But we think in some situations geometry can behave in an uncertain indefinite "quantum" way. For example at very small scale. Or in extreme conditions at the heart of a black hole.
The CDT researchers use a computer simulation to model small artificial quantum universes which they can study. What they do is a good place to start understanding the problem of how to get a quantum theory of geometry.
(gravity=the curvature of spacetime, is just one aspect of geometry, namely how geometry is affected by massive objects like the Earth and sun. To really do quantum gravity one must do quantum geometry.)
So start out by reading this:
http://www.signallake.com/innovation/SelfOrganizingQuantumJul08.pdf
Then after you have a taste of CDT we will know you better (from any questions you ask or comments uou make) and we can begin explaining LQG to you.
qinglong.1397 said:... I need this introductory material. Although I just graduated from an undergraduate school, ...
tom.stoer said:... ST is more ambitious than LQG and tries to unify all forces; it's not restricted to just one force.
You should have this always in mind when comparing the two research programs.
MTd2 said:In ST, quantum gravity relies on the existence of other fields, whereas LQG doesn't.
marcus said:...In fact the reviewer, Sahlmann, takes a restricted view of LQG, he only talks about one approach out of several that are being pursued by LQG community. This could be misleading if one takes his words out of context. Much of the action in LQG during the past 3 years has been in the area of spinfoam models and the application of LQG to cosmology. This is what Sahlmann does NOT discuss because those topics were assigned to other speakers at the conference.
qinglong.1397 said:It sounds that LQG community is divided into different group. um, feel bad...
qinglong.1397 said:It sounds that LQG community is divided into different group. um, feel bad...
Kevin_Axion said:atyy, which approach to Quantum Gravity do you prefer? Superstring Theory or LQG? I know Superstring Theory is an idea for a theory of everything but which is more convenient and elegant in your perspective?
atyy said:I'm partial to Xiao-Gang Wen's approach But AdS/CFT is definitely in the spirit of "emergence", and one that works technically too, so I find that fascinating. The parts of LQG I like are those that are more emergent in spirit, like Livine and Oriti's approach to group field theory, and Markopoulou's attempt at emergent locality.
MTd2 said:But you sound like a Green Dragon!
MTd2 said:I am a Brazilian, without imediate chinese ancestors! Well, maybe 14,000 years ago! :)
MTd2 said:Yes, a little bit! :) I need practice though. If you want to help me, send me a PM!
Kevin_Axion said:Private Message, just click on his user name to send it.
String Theory is a theoretical framework used in physics to explain the fundamental nature of particles and their interactions. It proposes that the building blocks of the universe are not point-like particles, but rather tiny, vibrating strings.
LQG, or Loop Quantum Gravity, is another theoretical framework used in physics to explain the fundamental nature of space and time. It suggests that space and time are not continuous, but rather made up of discrete, quantized units.
The main difference between String Theory and LQG is their approach to explaining the fundamental nature of the universe. String Theory focuses on particles and their interactions, while LQG focuses on space and time.
Currently, neither String Theory nor LQG has been experimentally proven, so neither can be considered more widely accepted in the scientific community. Both theories have their own strengths and limitations, and further research and experimentation is needed to determine their validity.
There is ongoing research and debate on whether String Theory and LQG can be combined or if they are fundamentally incompatible. Some scientists believe that they can be integrated into a single, unified theory, while others argue that their differences are too significant to merge them into one theory.